Georinex

File that took one minute to read now takes only 5 seconds.
This accomplished by using 3-D Numpy array preallocated by 10 ms fast prescan of OBS file.

Note: this module would previously issue an error, not just silently give bad results. Now it works correctly.

Thanks serioca fixes 25

Some RINEX writers leave gaps in SV names. instead of `G07` they write `G 7`, which making indexing messy.
Now they are renamed in `xarray.Dataset` for easy, efficient indexing.

* Enable Hatanaka compressed RINEX `.crx` and `.crx.gz` reading using stream processing via Hatanaka's `crx2rnx`--no temporary files are used
* simplify API with `georinex.load` convenience method
* speed reading by optionally specifying `meas=`

Add time reading from NAV files `TimeRinex`
Add several tests for handling of large NAV files
Add "use" option for RINEX 3 NAV files, to select specific satellite systems.

Improved multi-system RINEX 3 NAV files (Beidou, GNSS, GLONASS, Galileo, QZSS, SBAS)

Increased test coverage of NetCDF4 (HDF5) read/write

Failsoft more parts of code where user may not have every prereq